Rank: ? (34)
Member #: 10127

Is it possible to home-made a transciever/reciever (500m-5km) and attach it to ETH card in PC?

Rank: ? (1121)
Member #: 1689

Well, it's always possible. But, it would be extremely difficult. I don't think anyone other than misterhaan could help you there. You'll probably have to do a little research yourself.

Rank: ? (4827)
Member #: 3416

hey there's other people besides me who know this stuff

anyway i can't tell you everything you'd need to do in order to make ethernet run through the airwaves but here's a few things you'll have to consider:

- this is two-way communication, not just a single broadcast. this means you need a transmitter (broadcast) and receiver at each end.
- ethernet has 8 conductors (not all are necessarily used), so you will need to find which are used to transmit, and which to receive. the case might actually be that most of the conductors are bi-directional, which complicates your project further.
- it's easier to build an AM transmitter/receiver than an FM, so i'll talk about that. you need an oscillator that you can tune to the same frequency for each transmitter/receiver pair. you'd need at least one frequency for each direction, and they need to be spaced by at least twice the maximum bandwidth that you want to be able to transmit.
- speaking of bandwidth, say you want to run 10 Mbits/s through this system. that means if you choose to broadcast at 75 MHz for your outgoing traffic, it'll take up the range of 65 MHz through 85 MHz. then you need to make sure your incoming is lower than 55 MHz or higher than 95 MHz so that they don't interfere with each other. this means you're taking up a total of 4 times the bandwidth you
- then with frequencies, in the united states there's the fcc that you have to deal with because there's only so many useable frequencies out there and they're all in use already. the range you mentioned is enough that you could stomp on peoples radio / tv reception and that isn't legal.

as you can probably see, this is a large project that probably isn't ver feasible. While it may be possible, it's probably not worth it. Also, the points i've listed above are a good part of the reason you can't buy something right now that will do this. there's 802.11b or g, but those won't give you the range you're looking at. small radio stations get that kind of range, and you know what it takes for them to get a useable signal out that far. then again ham radio works for home users and has a pretty large range, so you might be able to find a way to send your data like that, but the bandwidth required for a human voice is in the range of 20 kHz, not 10 MHz . . .

Rank: ? (34)
Member #: 10127

I just wanted to bulid a small reciever and sender and connect them to BNC Connector (it looks like Cable TV connector- it has only 2 wires) of LAN card.
Maybe i could use 27 Mhz or something similar (40Mhz...).
But i have problems, because there are only two wires used for both in and out. So if I would connect reciever and sender to two cards ti would't ranscieve data, but it would only make high frequency beep. 8(

For small distances, you can only connect antenna to BNC connector.

Rank: ? (4827)
Member #: 3416

sorry, i thought from your first post that you were talking about ethernet. if you've already got cards with bnc connectors that go to an antenna, you just need to amplify the antenna. since it works short range with an antenna, that means that it's already mixed up to some RF level so that the antenna can send/receive it. so the two contductors are signal and ground.
still it's going to be difficult to get the range you were talking about, but you can at least boost it beyond what it is now. you could look into a pringles/soup can waveguide antenna for a cheap solution in that area. i'd give you more details but i haven't gotten into wireless communication much yet . . .

Rank: ? (1121)
Member #: 1689

My dad could probably help you there. He teaches in an Intro to Wireless class at Hopkins, but unfortunately he's in Australia now.

Anyways, are the signals out of the BNC ethernet a sine wave or just digital logic? You could easily modulate that onto an AM carrier using just a transfomer and a 1 Mhz oscillator. That's how I made my first AM radio, though the range is very poor unless it has a rather large antenna and a good ground. You simply connect the signal from the BNC connector to the transformer, which then goes to the power input of the oscillator. The output of the oscillator goes to your antenna.

Would you know of any ways to improve the range, misterhaan? This generally works for a few meters (2 or 3) but after that the signal quality drops off extremely quick.